1. Field of the Invention
The present invention relates to a Cognitive Radio (CR)-based broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for transmitting a Coexistence Beacon Protocol (CBP) packet in a CR-based wireless communication system.
2. Description of the Related Art
Developments in wireless communications have led to a situation where several types of communication systems coexist. Examples of the systems include a wireless communication system using a Code Division Multiple Access (CDMA) scheme referred to as a 2nd generation technique, a wireless communication system using an International Mobile Telecommunications (IMT)-2000 scheme referred to as a 3rd generation technique, and a system using an Orthogonal Frequency Division Multiple (OFDM) access scheme referred to as a 4th generation technique. In this situation, the coexisting systems use different communication schemes and provide services by using different frequency bands. However, since limited frequency resources are used for wireless communication, there is a problem in that the frequency resources are not enough to allow coexistence of a large number of systems.
Accordingly, there is ongoing research on a Cognitive Radio (CR) technique which uses a temporarily unused frequency band (or channel) among pre-allocated frequency bands in use. That is, even if a system is licensed for the use of a specific frequency band, the entire band is not always used. Therefore, the CR-based wireless communication system searches for a channel temporarily unused by a licensed system, and then provides a service through the found channel to User Equipments (UEs) within a service area. For example, temporarily unused frequency bands can be used among frequency bands allocated for transmission of a TeleVision (TV) signal.
When the wireless communication system uses the CR technique, Base Stations (BSs) that manage their respective cells have to share communication information for other BSs in order to effectively share frequency resources. For this, in the CR-based wireless communication system, BSs use a synchronized Self-Coexistence Window (SCW) slot to transmit a Coexistence Beacon Protocol (CBP) packet including their communication information to neighbor BSs, and the neighbor BSs share the communication information by receiving the CBP packet. The SCW slot is located in a predefined position in every frame. The CBP packet includes a variety of information related to a self-coexistence algorithm, for example, a location of a corresponding BS, a sensing result, scheduling information, a backup channel list, etc.
As described above, in the CR-based wireless communication system, BSs use an SCW to share information necessary for each cell by transmitting and receiving a CBP packet. However, since the SCW is a resource whose amount is limited, collision occurs when a plurality of BSs transmit the CBP packet. If the BSs fail to correctly receive the CBP packet from the neighbor BSs due to the collision in the transmission of the CBP packet, a system operation cannot be properly managed. Accordingly, there is a need for a method of transmitting and receiving the CBP packet without collision or errors to properly operate the CR-based wireless communication system.